1. Field of the Invention
The present invention relates to a recording and/or reproduction apparatus, and specifically to an optical disc on which recording tracks are continuously formatted by sample pits or pregrooves.
2. Description of the Prior Art
Among writable optical discs having a layer of a light sensitive medium, whose reflective index changes in response to the light, formed on the surface of the disc, there is a writable optical disc on which recording tracks are formed by sample pits or spiral pregrooves. FIGS. 1A, 1B and 1C show a plan view of such a writable optical disc and enlarged diagrams of recording tracks. In an optical disc, data areas D.multidot.A are formed by n sectors H.sub.1, to H.sub.n as shown in FIG. 1A.
In the case of pregrooves, as shown in FIG. 1B, the tracks are separated by pregrooves G. The head portions of the tracks are used as an area ADD.multidot.A of address data (51 bytes) which was preformatted by, for instance, an emboss process or the like. A total reflective area in which nothing is recorded is formed after the address data area ADD.multidot.A. L After an area M.multidot.A of the total reflective area (hereinafter, referred to as a mirror area), a data area D.multidot.A into/from which data can be actually written or read out is positioned.
In the case of an optical disc such that preformatted areas are formed by sample pits, as shown in FIG. 1C, two wobbling pits P.sub.1, and P.sub.2 and clock pits P.sub.3 are prerecorded. The mirror area M.multidot.A is formed between the wobbling pits P.sub.2 and the clock pits P.sub.3. The recording and/or reproduction apparatus of an optical disc is controlled so as to be always set into the reading mode in an area SSA or in the address data area ADD.multidot.A. In the data area D.multidot.A, a laser beam is controlled so as to write data in the recording mode and to read out the data in the reading mode.
A laser spot S irradiated from the optical head is subjected to position control via the tracking servo by the latter detecting the reflected light from the wobbling pits P.sub.1, and P.sub.2 or the pregroove G. In the ordinary recording or reproducing mode, the laser spot S is controlled so as to always pass down the center of the track. The mirror area (M.multidot.A) is provided to detect the power of the laser spot and the focusing state. By detecting the reflected light of the laser beam irradiating the mirror area, the optimum focusing servo can be applied and, in the reading, writing, or erasing mode, the intensity of the laser power can be controlled.
An optical head for a laser beam of such an optical disc is generally constructed by a biaxial actuator (fine actuator) to apply the focusing servo control and tracking servo control and a linear motor (coarse actuator) to move the fine actuator in the radial direction of the disc. To detect the reflected light from the disc surface, a two-part detector having two divided photo sensitive surfaces is used. By detecting a field image from the optical disc surface which is formed on the two-divided detector, using a push-pull method a tracking error signal can be detected.
When a target track on the optical disc is sought by the optical head as mentioned above, in general, a jump signal is supplied to the coarse actuator. The optical head is moved at a high speed to seek in the direction toward the inner track or toward the outer track on the optical disc, a laser beam is irradiated onto a target track, and data is read out or written at that point.
FIG. 2 shows an outline of a conventional driving circuit to execute such a seeking operation. Reference numeral 1 denotes a drive amplifier for a fine actuator 2, and 3 indicates a drive amplifier for a coarse actuator 4. In the ordinary recording or reproducing mode, a tracking error signal TE is supplied from a terminal a of a switch S.sub.1, through the drive amplifier 1 to a tracking coil of the fine actuator 2. The integrated voltage of the tracking error signal TE is also supplied to the coarse actuator 4 through a terminal a of the switch S.sub.2.
In the seeking operation to move the optical head to a target track, the switch S.sub.2 is switched and a seeking voltage S.sub.v is supplied from a terminal b of the switch S.sub.2 to move the coarse actuator 4 to the target track at a high speed.
The seeking voltage S.sub.v, comprises an accelerating voltage and a decelerating voltage in order to make the seeking speed high and has a drive waveform such that the optical head stops over the target track. However, generally, since an objective lens of the fine actuator 2 is supported so that it can oscillate, if the coarse actuator 4 is moved at a high speed, the objective lens oscillates extremely at the resonance frequency of the fine actuator 2. As a result, it is difficult to immediately start the tracking servo over the target track or at a position near it.
Therefore, for instance, as shown in FIGS. 2 and 3, there is proposed a method using a position sensor 5 (FIG. 2). The position sensor 5 detects the position in the radial direction of an objective lens L by irradiating a light P.sub.1, from the light source LS to an actuator A to drive the objective lens L and detecting the reflected lights P.sub.2 and P.sub.3 by detectors D.sub.1, and D.sub.2. During the seeking operation, while the switch S.sub.1, is switched, a position signal of the objective lens L is fed back from the terminal b through a coefficient circuit 6, and the vibration of the objective lens L is suppressed.
However, in such an apparatus, it is fairly difficult to provide the position sensor 5 for the small fine actuator. In addition, there is a problem such that by providing the position sensor 5, the optical head becomes expensive and the response characteristic of the fine actuator is deteriorated.